It is known in the art that the use of limited energy power sources has increased rapidly. Limited energy power sources are any energy source that has a limited energy capacity either by design or by its nature such as batteries, solar cells, fuel cells and even generators. These types of energy sources are at the heart of a number of electronic devices, such as, for example, cell phones, hand held games, and laptop computers. It is also known in the art that electric- and hybrid-electric-vehicles that use limited energy power sources, such as fuel cells, have a high cost to energy ratio. Similarly, lead acid batteries have a high weight to energy ratio. Such limited energy power sources point to the desirability to minimize the losses when providing energy to a load while increasing the energy supply between recharging or refueling periods in order to allow a user to operate the device or vehicle for longer durations.
A conventional power converter, which is the link between the energy source and load, tends to be a significant percentage of total system power loss, limiting the system efficiency, (i.e. the average output power divided by the average input power). Although the loss in efficiency may be as low as 5%, any loss limits or compromises the overall performance of the system. The loss in efficiency may be related to various parameters that include, but are not limited to, power consumption, switching frequency, temperature, component variations.
The temperature, for example, may be controlled to improve the efficiency by providing a heat sink for the power converter; however, the heat sink requires space thus, undesirably increasing the size of the electronic device. In many cases the heat sink is larger than the rest of the converter. In another example, size of the converter is also related to the switching frequency. For example, efficiency may be maximized when the switching frequency is reduced, which is achieved at the expense of more expensive and bulkier magnetic components and capacitors. Thus, there is a tradeoff and relation between size and the efficiency of the power converter.
Efficiency may change over the operating power consumption range (i.e. low power consumption, medium power consumption, and high power consumption). At low power consumption, the bias supply loss usually dominates the efficiency. For example, in a high frequency switching power supply, bias power is fixed and output power is reduced as the system operates at a lower power; therefore, the fixed bias power becomes a higher percentage of the overall total power loss, and, in some instances, when the system is operated at a relatively low power, the bias power may equal or exceed the output power. At the medium power consumption, switching losses dominate the efficiency formula, which are typically the source of most losses when both maximum output voltage across the switches and maximum current through them occur. At high power consumption, resistive losses dominate the efficiency formula.
In addition, the characteristics of the power components may vary when selected from a similar field of components. Even further, the power component tolerances (e.g. capacitive and inductive values) naturally change over time. Yet even further, physical changes to power components may occur over time as a result of being exposed to varying environmental conditions, such as temperature (e.g. varying environmental temperatures may have a detrimental effect on the insulative materials used in a component. Thus, physical changes and tolerance changes to power components may also result in a non-optimal application that was originally designed to operate at an optimal standard.
In most situations, power converters are normally optimized at a specific worst-case condition, such as, for example, maximum power consumption or highest operating temperature. In some situations, worst case condition efficiency optimization is set at a presumed operating condition that includes a combination of multiple parameters for example; operating at a high peak power for a short time, which relates to the peak operating temperature, for a system operating at 30% of the maximum power load. However, worse case condition settings may not always provide maximum efficiency if the system is not operated at the specific presumed settings. In a more application-specific example, a power converter efficiency optimization for a vehicular power brake system may include a worse case optimization for non-highway applications; conversely, the vehicle may be operated more often on a highway, thereby having shorter current duration periods and associated current surges that significantly decreases the optimization of the system. As a result, cost and size of the power brake system is increased as efficiency is decreased.
As understood from the explanation above, once the worst-case condition is defined, the process of optimization typically becomes a tradeoff between different design criteria (i.e. physical size of the electronic device and switching frequency). The end result is a static optimization at a presumed/predefined operating point, which typically occurs at maximum operational power and maximum temperature rating. This points to the deficiency of optimizing at one operating point in that the power converter may not operate at a presumably optimized point very often.
Conventional analog and digital controls cannot be designed to adapt to changing conditions without the additional cost of extra complicated circuitry. Even further, specific circuitry implemented for conventional analog and digital controls undesirably restricts functional monitoring of specific parameters for specific changing conditions. Even further, conventional analog and digital controls cannot adapt to constantly changing component tolerances. Thus, although adequate for monitoring specific parameters, conventional analog and digital controls undesirably restricts monitoring parameters and increases cost while also not considering dynamic changes in component tolerances.
Accordingly, it is therefore desirable to provide an ideal apparatus and method for efficiency optimization at every operating condition and component tolerance that can optimize power converter efficiency over the power converter's operating power range in an adaptive, dynamic manner.